I'm looking at upgrading my 30GB Vertex SSD for a 60+gb SSD. There seems to be really good words about C300 and excellent read speeds, but write speeds seems really low compared to Vertex 2? And what about Corsair Force serie 60gb?

Another consideration is whether you have SATA3 or not. Even the first-gen Sandforce in a Vertex2 is bottlenecked by SATA2. The C300 is a SATA3 drive and would be bottlenecked at less than 300MB/s if run at SATA2.

SATA3 is just a short-term patch anyway. It's almost obsolete even before it's been fully implemented. Multiple-controller SSDs have already surpassed its bandwidth. HSDL and other PCIe connections are the only way to go.